Hydrogel Contact Lens Refractive Index Measurement

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Solution Overview

Problem

Existing methods for determining the refractive index of soft contact lenses are inaccurate due to variable pressure and hydration issues during measurement, which are influenced by operator variability and the inability to maintain the lens in a submerged, saline state.

Innovation Solution

A critical-angle refractometer with a flat prism interface, a light source, and a photoelectric sensor, combined with a fixture that allows for precise placement and application of a hydrogel contact lens in a concavely shaped cavity with a predetermined pressure to maintain hydration and ensure consistent contact with the prism interface.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a typical refractometer is used to measure the refractive index of a contact lens, then the measurement can be performed, but the measurement accuracy deteriorates due to variable pressure and hydration of the lens during measurement

Engineering Contradiction:

Improverefractive index measurement accuracyVSAvoidmeasurement consistency

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent introduces an intermediary liquid (saline solution) between the refractometer prism and the contact lens. This liquid medium maintains the lens in a hydrated state during measurement, eliminating the dehydration problem that occurs with direct contact measurement. The liquid acts as a mediator that preserves the lens's natural optical properties while enabling the refractive index measurement.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent applies preliminary action by pre-hydrating the contact lens in saline solution before measurement and maintaining this hydrated state throughout the measurement process. The fixture is designed to hold the lens in a pre-conditioned state, ensuring consistent hydration levels before the actual refractive index measurement occurs.

Inventive Principle:

Principle #10Preliminary action

2Ease of operation

If operator manual handling is used for contact lens measurement, then flexibility is maintained, but operator variation significantly influences measurement results

Engineering Contradiction:

Improveoperator flexibilityVSAvoidmeasurement consistency

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent implements self-service through an automated fixture system that automatically positions the contact lens, applies consistent pressure, and maintains hydration levels without operator intervention. The fixture self-regulates the measurement conditions, eliminating operator variability while maintaining ease of use through simple lens placement followed by automated processing.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent replaces manual mechanical handling with an automated mechanical fixture system. The fixture uses mechanical components to automatically position the lens, apply consistent pressure through weights or springs, and maintain the lens in the measurement position, thereby eliminating the variability introduced by different operators' manual handling techniques.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If the contact lens is not submerged in liquid during measurement, then the measurement process is simpler, but the lens hydration becomes variable affecting accuracy

Engineering Contradiction:

Improvemeasurement process simplicityVSAvoidrefractive index accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent segments the measurement system into distinct functional components: a liquid reservoir for hydration, a fixture for mechanical support and positioning, and a refractometer for optical measurement. This segmentation allows the liquid submersion function to be independently optimized without complicating the overall measurement process, as each component performs its specific function independently.

Inventive Principle:

Principle #1Segmentation

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This method significantly reduces operator variation and ensures the hydrogel contact lens remains fully hydrated, resulting in more accurate and consistent refractive index measurements.

Implementation Method 1

a light source that radiates light to the interface surface and a photoelectric sensor for receiving light reflected from the interface surface

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 2

critical-angle refractometer to measure the refractive index

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 3

wherein the hydrogel contact lens maintains at saturating state by the liquid

Methodology Applied

Scientific EffectHydration: Absorption (physical)

Data Source

PatentUS10859465B2Method and apparatus for the measurement of the refraction index of a hydrogel contact lens

Publication Date: 2020.12.08 ALCON INC

AI summary

The invention is generally directed to an apparatus and a method for measuring a refractive index of a soft contact lens under a consistent pressure.